1. Field of the Invention
This invention relates to the field of membrane devices, and more particularly, to a disposable blood oxygenator of the membrane type.
2. Prior Art
It is well recognized in the medical arts that the need to oxygenate the blood, especially during extensive surgical procedures, is of great importance. The reason for the need for this oxygenation is because often times the patient's heart and lungs may either be out of action, such as during open heart surgery, or may be impaired due to a specific disease or the trauma of the surgery. Thus, the patient can only be kept alive if the heart and lungs are taken over by a machine in such a manner that the blood can be aerated and returned to the body. Various artificial heart and lung machines have been devised to accomplish this need. With respect to those machines designed to oxygenate the blood, they all tend to suffer from a number of different shortcomings which has lead to problems inherent in each device. Moreover, even in those few devices which properly oxygenate the blood, i.e. membrane-type oxygenators, they are extremely expensive and/or complex in nature. This, however, is not to be considered a great criticism of these prior art devices inasmuch as the actions taking place in the lungs on the blood is extremely complex. The fact that prior art devices are complex is therefore not surprising.
During surgery, the prior art devices designed to oxygenate the blood, circulated the venus blood (the blood which has had the oxygen removed and is now on its pathway back to the heart) through an oxygenator where oxygen is added, and preferably, carbon dioxide and other impurities are removed. The now oxygenated blood is then returned to the patient's artery (the arteries form the pathway through the body for blood which has been oxygenated). In the past, the oxygenator-of-choice is a device referred to as a bubble oxygenator in which the blood is brought into direct contact with oxygen. One problem with such device, however, is that the large blood-gas interfaces present in such apparatus are believed to damage the blood thereby limiting perfusion with such devices to relatively short time periods. In a membrane oxygenator, the oxygen and blood are separated by a membrane through which the oxygen to the blood and carbon dioxide from the blood diffuse and thus the problem associated with direct exposure of the blood to the oxygen is eliminated. On the other hand, bubble-type oxygenators are simple and especially for that reason they are widely used notwithstanding both their time limitation and the possible damage to the blood.
However, as the ability to perform more difficult operations increases, i.e. various forms of open heart surgery, organ replacement, and the like, the need for a device which can be used in the course of lengthy surgery, (five hours or more) has lead to the use of the more complex and costly membrane oxygenator. Further, it is presently believed in the art that membrane oxygenators also meet various other advantageous criteria. For example, they provide good gas transfer rates and tend to minimize the trauma to the blood, they do not require large priming volumes, they are more easily regulated in terms of blood flow to and from the patient, they enable oxygenation to take place without direct mixing of the oxygen with blood, and they may include various heat transfer means such that the blood can be selectively heated or cooled depending on the surgical procedure.
However, there are still a number of problems with membrane oxygenators. For example, the transfer of oxygen to the venous blood should balance the excretion of the carbon dioxide from the blood. One problem with prior art membrane devices was that the carbon dioxide diffused through the membrane at a different rate than the oxygen. Further, the blood may form a stagnant boundary layer adjacent the membrane. A membrane oxygenator designed to overcome these problems is described in U.S. Pat. No. 3,413,095. That oxygenator is described as being made up of a plurality of cells, each of which include a pair of spaced apart membranes between which the blood flows. A foraminous spacing member or screen is used to separate the membranes and to provide turbulence in the blood flow sufficient to break up or reduce the thickness of the boundary layer of blood adjacent to the membrane surface. Oxygen is caused to flow across the outer surface of the membranes and to diffuse into the blood. Various water mattresses or jackets are located on the outer sides of the membranes and are separated by foraminous spacing members through which the oxygen flows along the membrane. The water is maintained in the water jacket at a higher pressure than the blood and oxygen in such a manner that the membranes and blood and oxygen-spacing members are all clamped together into intimate contact so as to ensure a constant and small blood volume in each of the cells. A more detailed review of the U.S. Pat. No. 3,413,095 reveals, however, a device of relatively great complexity which suffers the shortcomings of being expensive, and therefore is generally taken apart, cleaned and reassembled with new membranes after each use.
In another prior art device disclosed in U.S. Pat. No. 3,564,819, a membrane oxygenator is shown which also configures a plurality of membranes so as to define a first and second group of flow volumes. Discontinuous channels extend transversely between adjacent membranes. Each channel places a pair of adjacent flow volumes of the same group into flow communication, while the gas-tight wall defining each channel bonds together the portion of the spacing means embedded therein and portions of the membranes located at each end of the wall. Again, a close analysis of the U.S. Pat. No. 3,564,819 reveals a device of substantial complexity, and while it may be good for the specific purposes taught therein, suffers significant shortcomings.
Yet another prior art device is disclosed in U.S. Pat. No. 3,834,544. That patent is directed to a membrane-type blood oxygenator of the disposable type, i.e. sufficiently inexpensive to manufacture so that it can be used once and discarded. The distinct drawback with such device, however, in addition to its complexity, is that it is susceptible to inadvertent leakage of the water into the blood. This presents a significant shortcoming in that when water mixes with blood, it can cause hemolysis which can be extremely harmful to the patient. Even the possibility of such catastrophe is sufficient to represent significant drawbacks with respect to any such device. In addition, a review of U.S. Pat. No. 3,834,544 will indicate that a plurality of clamps are needed to keep the various compartments leak-proof, but these cumbersome clamps present structural problems in addition to the other problems discussed hereinabove.
Other prior art devices are shown in U.S. Pat. Nos. 3,998,593, 3,979,297 and 3,520,803.
The present invention is directed to a membrane oxygenator of the disposable type which contains none of the aforementioned shortcomings discussed with respect to the prior art devices. The device of the present invention comprises a series of water modules and blood modules arranged in a predetermined configuration which are so designed as to substantially reduce the possibility of mixing of the water flow with the blood flow. The modular construction substantially reduces the number of parts, and the method of joining and sealing the various components and does away with cumbersome clamps. This enables the device of the present invention to be manufactured at a relatively low cost such that it can be disposed of after one use.